Quantum Dot Memory By Induced Strain

For over a century our daily lives are rapidly transformed by technology. Powerful electronic devices, such as home computers and mobile phones, became readily available in every household and now power our whole economy and infrastructure. With the ever-growing coverage and speed of the internet the areas of communication, science and trade experience another massive boost. All our current devices process, store and share data in the form of bits, which are the smallest chunks of information possible in classical physics. One bit can only have one of two possible values: zero or one. Quantum computers, in contrast, operate with quantum-bits, or qubits. Qubits can exist in any superposition between zero and one, and multiple qubits can be entangled with each other. This way of information processing unlocks enormous potential, which can not even in principle be reached by classical technology. Quantum technology could revolutionize secure communication, medical research and science in general, and these are only the applications we currently know about. Quantum technology, however, comes with its own sets of challenges. One persistent challenge is the storage of qubits. This arises from the inherent fragility of qubits, which are easily destroyed by interaction their environment. Moreover, qubits cannot simply be copied and amplified like classical bits, as this is forbidden by the laws of quantum mechanics. Without a proper way to store qubits, advances in quantum communication and -computation are strongly impeded. This project aims to tackle the storage problem. We use small structures in a semiconductor chip, so called quantum dots, with a size of only a few nanometres. It was demonstrated that, under well controlled conditions, these quantum dots can receive qubits in the form of light particles (photons), store them and send them back out with the push of a button in the form of another photon. This kind of storage is perfect for our existing communication infrastructure, which is already largely based on optical fibres. The University of Cambridge has the infrastructure and the expertise to identify the key requirements for a long-term storage of qubits in quantum dots. We use lasers and ultra-fast photon detectors to write and read qubits into and from a single quantum dot. To fully unlock the storage capabilities, we need to strain our chip with a micrometre sized piezoelectric actuator sitting directly under the chip. This manipulates the quantum dot so that it can shelve the received qubit into its ~100000 nuclei, and to read it back out on demand. We are constantly collaborating with theoreticians and material scientists across Europe to develop the ideal quantum dot platform with high efficiency and long storage times. A success would mark a huge leap towards practical quantum computation a global quantum infrastructure - a quantum internet.